Personally, I use a Garmin right now. A Garmin Nuvi 750 with a MSN account. I've fallen in love with this thing as it has helped me avoid various traffic jams, road work and less than ideal routes. This isn't a cheap unit, but it was a very good fit for my lifestyle and driving pattern.
I would highly suggest that you check out the links at the end of my post, especially
GPSTracklog. That site has a really helpful discussion of which kinds of GPS units fit various price points and driving habits.
Regardless of what kind of unit you get, make sure it allows you to update Points of Interest, and that it comes with relatively recent maps. The 2009 Garmin maps, for example, are already available.
I can strongly recommend the following applications/websites to help you get more out of your GPS:
GMapToGPX
(Allows you to convert Google Maps routes to routes you can download to your GPS)
POI Factory
(Points of Interest such as tourist attractions, rest stops, RED LIGHT CAMERAS, etc.)
GPS Tracklog